Apparatus, method and system for monitoring fluid

ABSTRACT

Fluid level in a container is determined using a single pressure transducer connected to a portable body. The body contains a computer having a memory in which fluid level-to-fluid volume conversion data are stored for different shapes of containers so that fluid volume can be readily obtained for the shape of the respective container once fluid level is determined. These features allow a single monitoring apparatus to be used for monitoring different types of containers. The apparatus preferably includes a radio so that multiple apparatus can communicate in a system with a central remote operator interface device. Fluid level is determined by dividing a pressure reading from the bottom of the fluid by a fluid density determined from two prior pressure reading taken across a known distance (density equals the difference between the two readings divided by the distance).

This is a continuation of copending application(s) Ser. No. 07/744,776filed on Aug. 14, 1991, now U.S. Pat. 5,211,678.

MICROFICHE APPENDIX

A microfiche appendix (3 sheets containing 209 frames) is incorporatedherein.

BACKGROUND OF THE INVENTION

This invention relates generally to apparatus, methods and systems formonitoring fluid in containers. The present invention relates moreparticularly, but not by way of limitation, to a radio-linked fluidmonitoring system incorporating apparatus and method that use a singlepressure sensor in a respective container to determine fluid level fromwhich fluid volume can be automatically determined for different shapesof container.

To maintain an adequate fluid supply for a process which draws fluidheld in a storage container, the amount of fluid in the containertypically must be monitored. In the oil and gas industry, for example, awell sometimes needs to be fractured to enhance its productivity.Fracturing fluid to accomplish this is typically stored in one or morestorage containers at the well site. The fluid is pumped out of thecontainers and into the well as needed. The operator in charge of thepumping needs to be aware of the various conditions of the pumping andfracturing process, one of which conditions is the amount of fluidremaining in the one or more containers.

One way to remain apprised of the amount of fluid is for the operator tovisually or otherwise locally inspect each fluid container. This is nota desirable technique because of the potential safety hazard of being onor around the containers to inspect them and because of the time itwould take to inspect the containers.

To alleviate the foregoing shortcoming, there are automated devices formeasuring fluid levels in containers. These can use various techniques,but the one relevant to our invention described below uses fluidpressure for determining the amount of fluid in the container. Thepressure responsive techniques we are aware of use two pressure sensorsto determine fluid level. One type uses one differential pressuretransducer to determine density and one gauge pressure transducer tosense pressure at the bottom of the body of fluid. Another type uses twogauge pressure transducers; outputs from the two pressure transducersspaced a known distance apart are used to compute density, and theoutput from one of the pressure transducers provides the total fluidpressure which is divided by the determined density to give a quotientspecifying the level of the fluid in the container. The transducers ofthese systems we are aware of are fixed to the containers (e.g.,attached to the side wall of the container below the surface of thecontained fluid) so that they cannot be readily moved (e.g., containermust be drained before transducers can be detached). Such systems canprovide for remote communications of data via wire or radio frequencytransmission.

Although the foregoing automated devices and systems can provideadvantages over types requiring local inspections by an operator, thereis still the need for an improved automated apparatus. There is the needfor a fluid monitoring apparatus which uses only a single pressuresensor, thereby obviating the cost of the second sensor used in theaforementioned devices. There is the need for a fluid monitoringapparatus which is easy to use with different types of containers. Forexample, the apparatus preferably should be portable and adaptable foruse with different shapes of containers. That is, the apparatus shouldbe able not only to calculate the height of the fluid in a container,but also to convert that height into the correct volume, which can bedifferent from one shape of container to another for the same calculatedheight. There is also the need for a fluid monitoring method and systemwhich meet these same needs and which permit remote communication andcontrol.

SUMMARY OF THE INVENTION

The present invention overcomes the above-noted and other shortcomingsof the prior art by providing a novel and improved fluid monitoringapparatus, method and system which meet the aforementioned needs.

The present invention provides an apparatus for monitoring fluid in acontainer, comprising: one, and only one, pressure sensor adapted to bemoved in the container and the fluid therein; and means for receivingsignals from the pressure sensor in response to, and as readings of,pressure sensed by the pressure sensor and for determining density ofthe fluid in response to two readings from the pressure sensor and fordetermining the level of the fluid in the container in response to thedetermined density of the fluid and a third reading from the pressuresensor. In a preferred embodiment, the present invention provides anapparatus for monitoring fluid in a selected one of a plurality ofdifferent containers, comprising: a reel adapted to be rotated relativeto a selected container; an electrical cable mounted on the reel; one,and only one, pressure sensing means for sensing pressure in the fluid,the pressure sensing means connected to the electrical cable; a batterydisposed in the reel; and electrical circuit means, connected to thebattery and disposed in the reel, for automatically determining,regardless of the shape of the selected container, the level and volumeof the fluid in the selected container in response to pressures sensedby the pressure sensing means throughout the fluid in the selectedcontainer as the pressure sensing means is moved within the fluid on thecable.

The present invention also provides a method of monitoring fluid in acontainer, comprising: (a) sensing with a pressure sensor the pressureof the fluid at a first depth of the fluid; (b) sensing with thepressure sensor the pressure of the fluid at a second depth of thefluid, which second depth is a known distance from the first depth; (c)sensing with the pressure sensor the pressure of the fluid at the bottomof the fluid; (d) determining the density of the fluid in response tothe pressures sensed in steps (a) and (b); and (e) determining theheight of the surface of the fluid in the container in response to thepressure sensed in step (c) and the density determined in step (d). Thismethod preferably further comprises determining the volume of fluid inthe container in response to the determined height, including retainingin a memory, located with the pressure sensor, conversion tablescorrelating volume with height for a plurality of containers, andretrieving from the memory the volume correlated with the heightdetermined in step (e) for the respective container.

The present invention further provides a fluid monitoring system,comprising: a plurality of fluid containers disposed at a well site; aplurality of fluid measuring devices, each of the devices mountedadjacent a respective container and each of the devices including: one,and only one, pressure sensor adapted to be moved in the respectivecontainer and the fluid therein and to provide signals in response topressure; computer means for receiving signals from the pressure sensorin response to, and as readings of, pressure sensed by the pressuresensor and for determining density of the fluid in the respectivecontainer in response to two readings from the pressure sensor and fordetermining the amount of the fluid in the respective container inresponse to the determined density of the fluid and a third reading fromthe pressure sensor; and a first radio connected to the computer means;and an operator interface device located remotely from the fluidcontainers and the fluid measuring devices, the operator interfacedevice including a second radio for communicating with each first radioto receive therefrom encoded signals representative of the amount offluid in the containers.

An advantage of the present invention is that it uses one, and only one,pressure sensor with regard to monitoring the amount of fluid in any onecontainer. Furthermore, the present invention is portable and is adaptedto monitor fluid in different shapes of containers. This adaptability isavailable in the apparatus which is located at the container. Thus,multiple container configurations can be accommodated with a single suchapparatus. The apparatus operates without requiring on-going directlocal control by an operator after the apparatus has been set-up andinitialized. This is desirable from a safety standpoint because no oneis required to be on or around the container or containers monitored bythe present invention (however, the preferred embodiment does permitsuch direct local control). Remote communications between a localmonitoring apparatus and a remote operator interface device arepreferably via radio links so that no cables need to be run across longdistances which might separate the apparatus and operator interfacedevice. This is particularly advantageous when several apparatus areused in combination with an operator interface device.

Therefore, from the foregoing, it is a general object of the presentinvention to provide a novel and improved apparatus, method and systemfor monitoring fluid in one or more containers. Other and furtherobjects, features and advantages of the present invention will bereadily apparent to those skilled in the art when the followingdescription of the preferred embodiment is read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and block diagram illustrating several apparatusof the present invention associated with containers and in radiocommunication with an operator interface device.

FIG. 2 is a front exterior view of the preferred embodiment of theoperator interface device.

FIG. 3 is a schematic circuit diagram of a modem circuit used in theoperator interface device for communicating with a fluid monitoringapparatus of the present invention.

FIG. 4 is a side view of the preferred embodiment of the fluidmonitoring apparatus of the present invention.

FIG. 5 is an end view of the apparatus shown in FIG. 4.

FIG. 6 is another end view of the apparatus shown in FIG. 4.

FIG. 7 is a schematic circuit and block diagram of the electricalfeatures of the apparatus shown in FIG. 4.

FIGS. 8A-8C are a schematic circuit diagram of the circuit for theprinted circuit board shown in FIG. 7.

FIGS. 9-14 illustrate various displays output by the operator interfacedevice during operation of the preferred embodiment apparatus, methodand system of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIG. 1, the fluid monitoring system of the presentinvention includes a plurality of fluid containers 2, a plurality offluid measuring devices 4, and an operator interface device 6 (differentunits of the same type of device are designated by the same referencenumeral but different letter). It is to be noted, however, that thepresent invention also pertains more generally to any one of the fluidmeasuring devices as a stand-alone apparatus. The overall system asillustrated in FIG. 1 will be described first, followed by descriptionsof the operator interface device 6, the fluid measuring device 4 and themethodology and operation of the present invention.

The fluid containers 2 can have different shapes and capacities. Flat-,angular- and curved-bottom containers are illustrated in FIG. 1 by wayof example.

Shown in FIG. 1 to be associated with each container 2 is a respectivefluid measuring device 4; however, one device 4 of the present inventioncan be used with more than one container. That is, each fluid monitoringdevice 4 of the preferred embodiment is portable so that it can becarried from one container to another, and each such device is able tocompute both the level (i.e., total height or depth) and the volume offluid in different shapes of containers. The device 4 can be associatedwith a respective container 2 in any suitable manner which allows aprobe 8 and connected electrical cable 10 to be unreeled from a reel 12and lowered to the bottom of the container. For example, the device 4can be connected to the container, it can be disposed above thecontainer, and it can be put on the ground beside the container.

Although each device 4 can function as a stand-alone unit, it can alsofunction with the operator interface device 6 so that, once the devices4 have been set up and initialized and the probes lowered to bottom, anoperator does not need to be physically located at the containers 2 ordevices 4 to be advised of the amounts of fluid in the containers 2. Inthe preferred embodiment, each device 4 communicates with the operatorinterface device 6 via a radio link illustrated in FIG. I by the fluidmonitoring device antennas 14 and the operator interface device antenna16. Communications are bidirectional, as indicated by double-arrow line18, in the preferred embodiment wherein the operator interface device 6polls each fluid monitoring device 4 to control when each device 4transmits signals encoded with information about the monitored amount offluid. The operator interface device 6 thus functions as both a displayterminal for displaying information from the devices 4 as well as acontroller for controlling any of the devices 4 being used; however, aspreviously stated, the operator interface device 6 is not necessary tothe local monitoring function performed by each fluid monitoring device4 individually.

Referring to FIGS. 2 and 3, the preferred embodiment of the operatorinterface device 6 will be described. The device 6 includes a keyboardand display panel 20 through which an operator inputs and receivesinformation. The panel 20 and the overall interface device 6 aresubstantially the same (differences will be described hereinbelow withreference to FIG. 3) as the Operator Interface Panel of the HalliburtonServices ARC System. The panel 20 includes alphanumeric keys 22,directional arrow keys 24, function keys 26 (scroll list key 26a, unitskey 26b, display key 26c, cursor key 26d, reset key 26e, enter key 26f)and display 28. In the preferred embodiment, the operator interfacedevice 6 can communicate with up to fifty fluid monitoring devices 4.

Communication in the preferred embodiment is by the aforementioned radiolink involving radio frequency signals transmitted between the operatorinterface device 6 and the active fluid monitoring devices 4 which arewithin range (e.g., 1-2 miles). It is this radio communicationcapability that distinguishes the device 6 from the typical OperatorInterface Panel (OIP) of the Halliburton Services ARC System. Thiscapability is implemented by adding the circuit and radio illustrated inFIG. 3 to the conventional OIP. In the preferred embodiment, theoperator interface device 6 includes a Maxon DM0530 data radio 30 (UHF,two watts, 467.8 MHz crystal) having the antenna 16. The device 6 alsoadditionally includes a 1200 baud frequency-shift keying (FSK) modemcircuit 32 connected to the radio 30 for properly formatting data to betransmitted by the radio 30 or received thereby.

Referring next to FIGS. 4-8, the preferred embodiment apparatus forimplementing the fluid monitoring device 4 will be described. Referringinitially to FIGS. 4-6, each device 4 includes one, and only one,pressure sensor 34 adapted to be moved in the container and the fluidtherein. The pressure sensor 34 is a pressure transducer contained inthe probe 8 connected at the end of the electrical cable 10 illustratedin FIG. 1. In a particular embodiment, the pressure sensing meansincludes a 0-10 psig submersible pressure transducer model PDCR950TIfrom Druck, Inc.

The pressure sensor 34 is supported by the cable 10 and the reel 12 uponwhich the cable 10 is wound. The cable is of suitable length toaccommodate the size of the containers 2 with which it is contemplatedto be used and to accommodate the electrical connections needed betweenthe pressure sensor 34 and the electrical circuit means contained insidethe reel 12 as subsequently described.

The reel 12 is adapted to be rotated relative to a selected container 2with which it is to be used. This allows the cable 10 to be unreeled andthe pressure sensor 34 to be lowered into the selected container 2. Thereel 12 has a hollow cylindrical body 36 which includes separate frontand rear compartments or housings 36a, 36b connected between two endmembers 38, 40 by a plurality of external tie rods 42. The cable 10 iswound around the body 36 and tie rods 42.

The front housing 36a is fluid tightly sealed against front end memberor panel 38 by an O-ring seal 41, and it is fluid tightly sealed againsta middle panel 43 by an O-ring seal 45. Fluid entry through the cable 10is prevented or limited by a desiccant cartridge (not shown) connectedwithin the cable 10.

The circular end member 38 supports a connector 44 for the antenna 14,and it supports a display 46 and switches 48, 50, 52 for providing localdisplay and control means. The circular end member 40 is connected to abearing 54 attached to a frame 56 so that the reel can rotate relativeto the frame 56 and an object to which the frame 56 is fixed (e.g., acontainer, the ground).

Contained in the hollow interiors of the main reel body 36 are a circuitboard 58, a radio 60 and a battery 62 as shown in FIGS. 4 and 7. Thebattery 62 energizes the electrical components and circuits within thereel 12. The battery 62 is housed in the compartment 36b; it issupported by a bracket assembly 64 (FIG. 4). The printed circuit board58 and the radio 60 are housed in the compartment 36a. With regard tothe preferred embodiment circuits of the board 58 as shown in FIG. 8,the battery 62 is connected to the power regulating and switchingcircuit 63 (FIG. 8C). The battery 62 is preferably rechargeable, whichis provided for in the FIG. 7 embodiment through recharger connector 61mounted on the front end panel 38.

Contained on the circuit board 58 are electrical circuit means forautomatically determining, regardless of the shape of the selectedcontainer 2, the level and volume of the fluid in the selected containerin response to pressures sensed by the pressure sensing means 34throughout the fluid in the selected container as the pressure sensingmeans is moved within the fluid on the cable 10. This includes means forreceiving signals from the pressure sensor in response to, and asreadings of, pressure sensed by the pressure sensor and for determiningdensity of the fluid in response to two readings from the pressuresensor and for determining the level of the fluid in the container inresponse to the determined density of the fluid and a third reading fromthe pressure sensor.

Referring to FIG. 8A, the signal from the pressure sensor 34 is receivedthrough the cable 10 by a signal conditioning circuit 66. Theconditioned signal output from the circuit 66 is provided to a dualchannel multiplexer 68. Another input of the multiplexer 68 is connectedto a circuit 70 monitoring the voltage "VSWITCH."

Referring to FIG. 8B, a microprocessor-based microcontroller 72,responsive to a program stored in a preprogrammed memory 74, selects thechannel of the multiplexer 68 to be output to an analog-to-digitalconverter 76. The digital output from the analog-to-digital converter 76is communicated to the microcontroller 72 via a data bus 78. When thesignal received by the microcontroller 72 is one representing sensedpressure, it is stored in a random access memory internal to themicrocontroller 72. The stored signals are used to determine density andfluid level as subsequently described. The term "memory" as used hereinencompasses both the aforementioned memories of the preferredembodiment.

The electrical circuit means also includes means for converting thedetermined fluid level into a signal representing the fluid volume. Thismeans includes the memory 74 because it contains signals encoded todefine volumes correlated to heights of fluid for the plurality ofdifferent shapes of containers with which the device 4 is preset. In aparticular implementation, the memory 74 is programmed with a tablecorrelating fluid volumes (e.g., gallons) to fluid heights (e.g.,inches) for fifteen different shapes of containers; however, additionalshapes can be accommodated by additional preset memory or by manualentries using the microcontroller 72.

In view of the microcontroller 72 and the programmed memory 74, theforegoing are implemented at least in part by computer means forreceiving signals from the pressure sensor in response to, and asreadings of, pressure sensed by the pressure sensor and for determiningdensity of the fluid in the respective container in response to tworeadings from the pressure sensor and for determining the amount of thefluid in the respective container in response to the determined densityof the fluid and a third reading from the pressure sensor. Specifically,fluid height is calculated by the microcontroller 72 from the pressurereadings, and fluid volume is determined from the conversion tables inthe memory 74. Local external operation of the microcontroller 72 iseffected via the switches 48, 50, 52 (FIGS. 6 and 7) connected to themicrocontroller 72 via a connector 79 (FIG. 8A).

The locally computed data indicating the amount of the monitored fluidcan be communicated to a remote location by the radio 60 (FIG. 7) whichprovides means for transmitting an encoded signal representing thedetermined fluid level (and/or fluid volume). The radio 60 is disposedin the reel 12 and connected to the electrical circuit means so thatencoded signals representing at least the determined level of fluid canbe transmitted by the radio 60 to a location remote from the apparatus.For the preferred embodiment circuit shown in FIG. 8, the radio 60 isconnected to and controlled by the microcontroller 72 and modem 80 (FIG.8B). Connections with the radio 60 are made through a connector 82 andintervening circuitry as shown in FIG. 8A.

Computed data can be displayed locally through the display 46 whichprovides means for selectably displaying the microcontroller-determinedfluid level and the memory-stored correlated volume. The display 46 isconnected by conductors 84 (FIG. 7) and connector 86 (FIG. 8A) to thedata bus 78 and power components as shown in FIG. 8A. The display 46 ismounted on the end panel 38 of the reel 12 as described above.

Use of the fluid monitoring apparatus just described, and the method ofthe present invention, includes sensing with the pressure sensor thepressure of the fluid at a first depth of the fluid. In the preferredembodiment, this includes moving the single pressure transducer 34 tothe upper surface of the fluid in the selected container 2 by suspendingthe single pressure transducer 34 on the electrical cable 10 from thereel 12, and recording the pressure sensed at the surface. The sensedpressure is stored as an encoded signal in the memory of themicrocontroller 72 contained inside the reel 12.

The method further comprises sensing with the pressure sensor thepressure of the fluid at another depth of the fluid which is a knowndistance from the first depth. In the preferred embodiment, thisincludes lowering the single pressure transducer 34 a predetermineddistance (e.g., three feet) into the fluid in the container 2 byunreeling an additional length of the cable 10 from the reel 12. Thissecond sensed pressure is recorded by storing a second encoded signal inthe memory of the microcontroller 72 contained inside the reel 12.

The method of the present invention further comprises sensing with thepressure sensor the pressure of the fluid at the bottom of the fluid. Inthe preferred embodiment, this includes lowering the single pressuretransducer 34 to the bottom of the fluid by unreeling more of the cable10 from the reel 12 until the single pressure transducer 34 is on thebottom of the container. The pressure sensed at the bottom is recordedby storing a third encoded signal in the memory of the microcontroller72 contained inside the reel 12.

The method further comprises determining the density of the fluid inresponse to the pressures sensed at the first depth (e.g., at thesurface) and at the second distance, (e.g., a predetermined distancebelow the surface). In the preferred embodiment, this includes using themicrocontroller 72 inside the reel 12 for computing from the first andsecond encoded signals the quotient obtained by dividing (1) thedifference between the recorded pressures sensed at the surface and atthe predetermined second depth by (2) the predetermined interveningdistance.

The method further comprises determining the height of the surface ofthe fluid in the container in response to the pressure sensed at thebottom of the container and the density determined as just described. Inthe preferred embodiment, the height is determined using themicrocontroller 72 inside the reel 12 for computing the quotient of therecorded pressure defined by the third stored encoded signal divided bythe previously calculated density.

The method further comprises determining the volume of fluid in thecontainer in response to the determined height. This includes retainingin the memory 74 conversion tables correlating volume with height for aplurality of shapes of containers, and retrieving from the memory 74 thevolume correlated with the height determined as just described. In thepreferred embodiment, the microcontroller 72 inside the reel 12 isprogrammed for retrieving from the stored table contained in the memory74 for the particular container 2 a respective encoded signalrepresenting the volume correlated to the computed height and theparticular container.

In the preferred embodiment, the method further comprises transmittingan encoded radio frequency signal representing the determined height toa location remote from the monitored container. In the preferredembodiment, the transmission is made from the radio 60 as directlycontrolled by the microcontroller 72 and modem 80, but such directcontrol is not initiated in the preferred embodiment until a radiofrequency control signal is received by the microcontroller 72, throughthe radio 60, from the location remote from the container and fluidmonitoring apparatus (i.e., from the operator interface device 6 in thepreferred embodiment).

The foregoing general methodology and the following more specificmethodology can be implemented by programming the microcontroller 72with a program written using known programming skills to implement theprocedure described herein and stored in known manner in the memory 74.An example of such a program is listed in the microfiche appendixincorporated herein.

A more detailed explanation of the operation of a particularimplementation of the operator interface device 6 and the fluidmonitoring devices 4 follows. Although the utility of the presentinvention in its broader aspects is not limited to the oil and gasindustry, the following more detailed description will be made withreference to the containers 2 being tanks holding fracturing fluid at awell site. Such tanks and use are well-known in the industry. Althoughthe present invention is not so limited, typically there would be up toten or so such tanks at a well site. Again without limiting the presentinvention, examples of such tanks include: Adams Frac Master 500 BBL;Adams Frac Miser 500 BBL; Halco Round Bottom 500 BBL; Halco DBL CompRound Bottom Front; Halco DBL Comp Round Bottom Rear; Halco Flat Bottom500 BBL; Halco DBL Comp Flat Bottom Front; Halco DBL Comp Flat BottomRear; Haltank 75; Haltank 160; Haltank 345; Haltank 549; Sem CorpV-Bottom 500 BBL; Trailmaster Eliptical Bottom 500 BBL; and V.E.Enterprises V-Bottom 500 BBL.

A particular aspect of the preferred embodiment system is that itoperates in a master-slave mode. If the operator interface device 6 isused, it is the master device. The fluid monitoring apparatus 4 are theslave devices. Thus, each fluid monitoring apparatus 4 will transmit itsinformation only when it is polled by the master operator interfacedevice 6. To avoid communication confusion, only one operator interfacedevice 6 should be active (transmitter on) in the system at any onetime.

When the ARC-compatible preferred embodiment operator interface device 6is first powered up, its screen's appearance is very similar to ARCoperator interface panels (OIPs). There are two major differences:

(1) there will be no unit controller truck number to select since theoperator interface device 6 itself will function as a controller in thepresent system; and

(2) the message "WAIT. . . CHECKING RF SIGNALS" will be present for nomore than 20 seconds after power up in order for the operator interfacedevice 6 to determine if there are any other operator interface devices6 on and transmitting. This is a safeguard against multiple operatorinterface devices 6 acting as masters. However, the operator should makesure that there is only one master operator interface device 6transmitting at one time.

FIG. 9 shows the Display Select Menu which lists various other screensthat can be displayed through the display 28 of the preferred embodimentoperator interface device 6. The various screens can be displayed bypressing and holding the display button 26c (FIG. 2) and pressing thedesired letter key corresponding to the letter shown on the left of thelist in FIG. 9.

FIG. 10 shows the Display Select Menu for the various screens after thefluid monitoring apparatus 4 for some tanks have become active (tanksnumbered 1-4 in this example). Notice the difference between this screenand that of FIG. 9. A tank level selection has been added (selection A).Note also that the tank numbers of the active tanks are listed innumerical order at the right (1, 2, 3, 4). Thus this screen separatesthe active and inactive tanks via a separate tank level column. Theoperator can distinguish between which selection will display the statusof active tanks and those of the inactive tanks.

If the Tank Level screen is desired, press either the main display key26c (FIG. 2) or if there are more than one tank level selection, pressand hold the display key 26c and the selection letter. (In the example,pressing the display key 26c and the "A" key of alphanumeric keys 22will display the Tank Level screen and pressing the display key 26c andthe "B" key will display the Tank Status screen of the active tanks.)

FIG. 11 shows the Tank Level screen. This screen can be called only ifthe fluid monitoring device 4 for the respective tank has answered theoperator interface device 6 or if the operator has entered (defined) atank type, fluid type, or additive concentration.

Key features of the Tank Level screen are:

1) VOLUME--the volume of fluid remaining in a particular tank based onits defined tank type.

2) STATUS--the condition of the communication between the operatorinterface device 6 and the fluid monitoring device 4 for thecorresponding tank.

3) BAR GRAPH--graphical indication of the amount of fluid left in atank. The bar will update each time a data message has been receivedfrom the fluid monitoring device 4 for the corresponding tank.

4) VOLUME REMAINING ON LOCATION--the total volume of all active tanks.

5) VOLUME IN TANKS DISPLAYED--the volume of the tanks shown on thisscreen.

FIG. 12 shows the Tank Status of the tanks that have become active (inthis example, tanks numbered 1-4). Key features of the displayedinformation include:

1) POLL TIMER--when this timer counts down to zero, the operatorinterface device 6 will transmit a radio message to the correspondingfluid monitoring device 4. The fluid monitoring device 4 will thenanswer back in about a half second. When the operator interface device 6transmits a message, the MSGS SENT counter will increment by one. Whenthe operator interface device 6 receives a message from a fluidmonitoring device 4, the MSGS RCVD counter will increment by one. If theoperator interface device 6 transmits a message, it expects a message inreturn. If the operator interface device 6 does not get a message backwhen it expects it, it will signal a fault condition and retry thetransmission up to three (3) times. The number of counts that the polltimer counts down from is a function of the rate of change of the levelin the tank. If the tank level is constantly changing, then the polltimer will have a very short count (5 seconds is the shortest extreme).If the tank level is not changing very much, then the poll timer willgradually have longer counts. If the tank level stays constant longenough, the operator interface device 6 will eventually put therespective fluid monitoring device 4 in sleep mode for at most fourminutes and 15 seconds. Once a device 4 is in sleep mode, it will nottransmit level information until it is awake.

2) TANK TYPE--this tells both the operator interface device 6 and thefluid monitoring device 4 which type of tank is being used so thatappropriate selections are made from the memory 74 in the fluidmonitoring device 4 to determine the tank volume given a calculatedlevel of fluid. The tank type is entered by the operator. The cursor key26d and the directional arrow keys 24 (FIG. 2) can be used to go fromfield to field. Once the cursor is on the tank type field, the scrolllist key 26a (FIG. 2) can be held down and the up and down arrow keys ofthe keys 24 can be used to scroll through the various tank types. Withthe scroll list key 26a still pressed, the enter key 26f (FIG. 2) can beused to make the selection. Once the selection is made, the operatorinterface device 6 will transmit the tank type information to the fluidmonitoring device 4 for the respective tank on the next poll timerexpiration.

3) FLUID TYPE, ADD CONC--these fields are used primarily to displayinformation about the tank and its contents. They serve no operationalpurpose at the present time and can be left undefined if the operatorwishes.

4) BATT STATUS--this is the status of the rechargeable battery insidethe fluid monitoring devices 4. It should be at approximately 12 voltsfor proper operation.

5) SPEC GRAV--this field will be updated only if the tank was calibrated(zeroed and spanned across the predetermined distance between theaforementioned first and second depths) via the operator interfacedevice 6. If the tank was calibrated locally at the respective fluidmonitoring device 4, this field will not be updated. This field givesthe calculated specific gravity of the fluid given the zero and span.

6) TIMER--the timer will count up to 90 seconds. The operator interfacedevice 6 will then transmit a radio frequency message to the fluidmonitoring device 4 of the corresponding tank and if there is no answer,the timer will be reset to zero and it will count up to 90 again. If afluid monitoring device 4 answers, then the screen will automaticallyswitch to the Tank Level page and the corresponding tank will be placedon the active tanks list. For tanks on the active tanks list, the timerwill count up and will not reset to zero until the next message isreceived from the respective fluid monitoring device 4 (as a result ofthe aforementioned expired poll timer and the resulting polling by theoperator interface device 6).

7) COMM STATUS--this will indicate to the operator the condition of thecommunication between the operator interface device 6 and the fluidmonitoring device 4 of the corresponding tank.

8) MSGS SENT--this will keep track of the number of transmissions thatthe operator interface unit 6 has tried. Each time the TIMER is reset tozero, this counter will increment indicating that a radio frequencymessage was transmitted.

To control remote calibration, a screen as illustrated in FIG. 13 isprovided for entering the following data:

1) TANK NUMBER--this field determines which of the tanks (numbered 1-50)will be zeroed or spanned. To enter a number, press the cursor key 26dand the appropriate up and down arrow keys 24 to move to this field.While holding the cursor key 26d down, press the appropriate numerickeys and press the enter key 26f. The tank number is necessary only tozero or span. Once the tank number is entered, the message "ready toaccept commands" will be displayed on the screen.

2) ZERO--after entering the tank number of the tank to be zeroed, thetank can be zeroed at 0 (or any feet) by holding the cursor key 26d andentering the desired zero value and pressing the enter key 26f. Once thezero command is entered the message "zero command waiting to be sent."will be displayed and the operator interface device 6 will transmit thecommand at the expiration of the poll timer. When the respective fluidmonitoring device 4 receives the command, it will echo the command backto the operator interface device 6 and the operator interface device 6will display the new zero to the right of the zero field. This feedbackwill indicate that the fluid monitoring device 4 has received thecommand correctly.

3) SPAN--a tank can be spanned at some value (in feet) by holding thecursor key 26d and entering the desired span value and pressing theenter key 26f. Once the span command is entered, the message "spancommand waiting to be sent." will be displayed and the operatorinterface device 6 will transmit the command at the expiration of thepoll timer. When the fluid monitoring device 4 receives the command, itwill echo the command back to the operator interface device 6 and theoperator interface device 6 will display the new span to the right ofthe span field. This feedback will indicate that the device 4 hasreceived the command correctly.

4) SET RF TANK NUMBER--the operator interface device 6 can be used tochange the tank number of a particular tank. To do so, cursor down tothis field and enter the new tank number making sure that the fluidmonitoring device 4 to be changed is the only one on. This is importantbecause the command to change the tank number is a global command andthus all fluid monitoring devices that are on will receive it. Hence ifmore than one tank is on, those tanks will have the same tank number.

5) TURN OFF ALL UNITS--the operator interface device 6 can be used toturn off all the fluid monitoring devices 4 remotely. To do so, simplycursor down to this field and press the enter key 26f. There are nonumbers to type in--this is a global command and thus all listeningfluid monitoring devices 4 will turn off.

6) LOCAL RF TRANSMITTER--this field allows the operator to turn thetransmitter on the operator interface device 6 either off or on. Caremust be exercised when turning the transmitter on (or off) due to thefact that radio frequency conflicts can occur if more than one operatorinterface device 6 is being used. This is due to the need that thereonly be one master in a master-slave system.

FIG. 14 shows the screen for entering a fluid height-to-fluid volumeconversion table for a tank not previously included in the memory 74. Inthe present particular embodiment, the tables for the additional tanktypes are not supported in the memory 74 due to memory constraints. Whenthe tank type on the operator interface device 6 is different from thetank type on the fluid monitoring device 4, the volume displayed on theoperator interface device 6 does not correspond with the volumedisplayed on the fluid monitoring device 4. The level of fluid (ininches or meters) should be the same, however. Use the cursor key 26d,the arrow keys 24, and the numerical keys to enter the height (in inchesor meters from the bottom of the tank) and the volume corresponding tothat height. The data will be sorted by height after each pair of datapoints is modified and entered.

As stated before, the fluid monitoring devices 4 are considered slavedevices in a master-slave system. As a result, each fluid monitoringdevice 4 does not transmit any information until it has received arequest from the master operator interface device 6. On the topright-hand side of the 2-line LCD screen 46 of each fluid monitoringdevice 4, there is a status field that tells the operator the currentcondition of the fluid monitoring device 4. The messages displayed therecan be any one of the following:

1) ID--this message, which stands for idle, indicates that the fluidmonitoring device 4 has turned off its transmitter. There are tworeasons for the fluid monitoring device 4 to display this message:

a) the operator interface device 6 has issued a sleep command and thefluid monitoring device 4 is in sleep mode. As noted earlier, sleep modeis issued when the level in the tank stays constant for a long period oftime (about 14 minutes). This mode is mainly used for battery powerconservation.

b) the fluid monitoring device 4 does not recognize or "hear" anycommunications from any device (operator interface device 6 or otherfluid monitoring device 4). This condition arises when there is nooperator interface device 6 or there is a communications problem betweenthe operator interface device 6 and the fluid monitoring device 4 thatprevents the fluid monitoring device 4 from "hearing" anything.

2) BLANK--If this field is blank, then the fluid monitoring device 4 isusually in a normal operating mode. It "hears" messages from otheroperator interface device 6-fluid monitoring device 4 communications andit has not received a command to go to sleep.

3) TX--this message, which stands for transmit, comes up when the fluidmonitoring device 4 receives a message and it is transmitting a messageback. The TX message will disappear as soon as the message has beensent.

The following is how to operate a respective fluid operating device 4:

MEASURE FLUID LEVEL

a) Place the probe 8 into the fluid to be measured, allowing the probeto reach the temperature of the fluid.

b) Raise the probe 8 out of the fluid and press the key 50 on the end ofthe reel 12 to "zero" the unit. This calibrates the zero inches of fluidreading.

c) Lower the probe 8 until a float attached to the cable 10 is felthitting the top of the fluid and press the key 50 to "span.". This isthe second calibration point.

d) Drop the probe 8 to the bottom of the tank.

CALIBRATION OF SPECIFIC GRAVITY

Repeat the operations procedure above in a tank of water (specificgravity of 1). Press the "advance display" key 52 until the second linereads "set s.g. to water (1)". Pressing the "span" key 50 will set thespecific gravity to one. Calibrating on any other fluid will calculatethe specific gravity of that fluid as compared to this calibration ofwater.

Selecting the tank type

Several tank types are defined in the memory 74 of the device 4. Thetank type can be selected by selecting the tank type on the operatorinterface device 6 or locally on the fluid monitoring device 4 by:

a) Advancing the display (pressing the "advance display" key 52) to readout the volume of fluid and a tank type; or

b) Pressing the key 50 until the desired tank type is displayed.

Spanning the sensor somewhere other than at the float

The sensor can be zeroed or spanned at any depth from the operatorinterface device 6. Locally the sensor can be spanned at any depth from1 to 9 feet by:

a) Advancing the display (pressing the "advance display" key 52) untilthe second line reads "press span at x feet".

b) Pressing the key 50 to "zero" will advance the depth from 1 to 9feet.

c) Pressing "span" on key 50 with "press span at 9 feet" will span thesensor at 9 feet assuming the probe is 9 feet below the surface of thefluid.

Local bar graph indication

A local bar graph can be displayed by pressing "reset" on the key 58 orby pressing the "advance display" key 52 until the second line shows ahorizontal bar graph or is blank. This bar graph is in inches with onecharacter equal to 5 inches.

Changing units

The units can be changed from inches to meters and meters to inches by:

a) Advancing the display (pressing the "advance display" key 52) untilthe second line reads "chg units".

b) Pressing the key 50 to "SPAN."

Battery status

The status of the 12-volt rechargeable battery can be checked by:

a) Advancing the display until the second line reads "x-tank xx.x-V"where x is the tank number and xx.x is the voltage of the battery.

b) The voltage should be kept at 12 volts or higher for proper operation(using the battery charger).

Changing the tank number

The tank number may be changed by:

a) Advancing the display until the second line reads "x-tank xx.x-V"where x is the tank number and xx.x is the voltage of the battery.

b) Pressing the key 50 to "zero" advances the ones place on the tanknumber; pressing the key 50 to "span" advances the tens place on thetank number.

Pressure and specific gravity readings

Advancing the display until the second line reads "x.xx-PSI X.XXXX-SG"gives the pressure reading of the transducer (x.xx) and the specificgravity (X.XXXX).

Analog to digital converter reading

Advancing the display until the second line reads "xx.-A/D reading"gives the analog to digital conversion of the transducer signal. Theconverter is a 12-bit A/D, thus the range of the display will be from 0to 4095.

Thus, the present invention is well adapted to carry out the objects andattain the ends and advantages mentioned above as well as those inherenttherein. While a preferred embodiment of the invention has beendescribed for the purpose of this disclosure, changes in theconstruction and arrangement of parts and the performance of steps canbe made by those skilled in the art, which changes are encompassedwithin the spirit of this invention as defined by the appended claims.

What is claimed is:
 1. An apparatus for monitoring fluid in a selectedone of a plurality of different containers, comprising:a reel adapted tobe rotated relative to a selected container; an electrical cable mountedon said reel; one, and only one, pressure sensing means for sensingpressure in the fluid, said pressure sensing means connected to saidelectrical cable; a battery disposed in said reel; and electricalcircuit means, connected to said battery and disposed in said reel, forautomatically determining, regardless of the shape of the selectedcontainer, the level and volume of the fluid in the selected containerin response to pressures sensed by said pressure sensing meansthroughout the fluid in the selected container as said pressure sensingmeans is moved within the fluid on said cable.
 2. An apparatus asdefined in claim 1, wherein said electrical circuit means includes amemory containing signals encoded to define volumes correlated toheights of fluid for the plurality of different containers.
 3. Anapparatus as defined in claim 1, further comprising display means,mounted on said reel and connected to said electrical circuit means, forlocally displaying at the reel at least a selected one of the determinedlevel and volume.
 4. An apparatus as defined in claim 1, furthercomprising a radio disposed in said reel and connected to saidelectrical circuit means so that encoded signals representing at leastthe determined level of fluid can be transmitted by said radio to alocation remote from said apparatus.
 5. An apparatus as defined in claim4, wherein said electrical circuit means includes a memory containingsignals encoded to define volumes correlated to heights of fluid for theplurality of different containers.
 6. An apparatus as defined in claim5, further comprising display means, mounted on said reel and connectedto said electrical circuit means, for locally displaying at the reel atleast a selected one of the determined level and volume.